Especially given the shooter printed parts of the weapon and had no cellphone on them when they shot Brian McEvilCEO or whatever his name was. And then hopped on a scooter and left the island without a trace. So much planning went into the prep and, ahem, execution of the plan that holding into blatant evidence like a signed confession 2 days after the fact doesn't make any sense. It screams planted evidence on a person who vaguely looked like the only screenshot I've ever seen of the ahooter smiling.
At the very least I have very reasonable doubts and would not be selected for the jury.